In recent years, optical semiconductor devices have been made to have a higher output and brightness. Then, optical lenses and encapsulants that encapsulate each optical semiconductor element used in such optical semiconductor devices have increasingly been required to have further higher transparency, heat resistance, and light resistance. Meanwhile, electrode corrosion causes a problem such as a decrease in luminous intensity over time, so that excellent gas barrier properties against corrosion gas including, as representative examples, sulfur compounds such as SOx and H2S have been required at the same time.
As encapsulants for optical semiconductor devices, in particular, for high brightness and high current lighting applications, mainly used are methyl silicone (methyl silicone-based encapsulants) excellent in heat resistance and light resistance (see, for example, Patent Literature 1).
Also, widely used are phenyl silicone-based encapsulants having relatively good gas barrier properties against corrosive gas (see, for example, Patent Literature 2).